As is the case with Cortana on Windows Phone 8.1, Cortana will be an app, not part of the operating system itself, Neowin's Brad Sams said.

Cortana takes its codename from Cortana, an artifically intelligent character in Microsoft's Halo series who can learn and adapt. Cortana relies on machine-learning technology and the "Satori" knowledge repository powering Bing to learn what users want to find, track and do. Cortana is Microsoft's alternative to Google Now and Apple's Siri. Microsoft is in the midst of broadening Cortana availability through a variety of alpha and beta programs worldwide.

Cortana is core to Microsoft's makeover of the entire "shell" -- the core services and experience -- of the future versions of Windows Phone, Windows and the Xbox operating systems. Making Cortana available across all three platforms fits in with Microsoft's 'One Windows' strategy.

Microsoft has been working on making a personal digital assistant available as part of Windows since 2011, if not before. Officials promised scenarios where users would be able to tell their PCs to "print my boarding pass on Southwest" and have their systems automatically jump into action. The magic behind the scenes would be a combination of Microsoft Bing, Tellme speech technology and some natural-language-plus-social-graph concoction. (Microsoft moved its speech team into its Online Services unit, seemingly to facilitate work with the Bing team, at the very end of 2011.)